The RAF was inflicting such heavy losses on the Luftwaffe that Hitler decided to switch tactics in September; ordering a reduction in the number of daylight raids and the initiation of nighttime raids, which were more terrifying for the civilians being bombed, but less accurate and effective militarily.

At around 4:00 PM on September 7, 348 German bombers escorted by 617 fighters blasted London until 6:00 PM. Two hours later, guided by the fires set by the first assault, a second group of raiders commenced another attack that lasted until 4:30 the following morning.This was the beginning of what became known as the "The Blitz" (from the German for "lightning"), a campaign of intense bombing of London and other cities aimed at crushing British morale. The Blitz, which continued until May 1941, consisted of more than 70 attacks during which the Germans dropped more than 35,000 tons of bombs.

London was attacked repeatedly and terrified residents were forced to sleep in shelters; some retreated, against the wishes of the government, to the underground subway stations. At its peak, 177,000 people spent the night underground. Nearly half a million children were sent for safekeeping to homes outside London. The danger was real. In just one week in mid-October, for example, more than 1,300 Londoners were killed in German attacks.

In the worst single incident in the Blitz, 450 were killed when a bomb hit an air raid shelter at a school in West Ham. The most infamous raid during the Blitz occurred on November 14, 1940, when 500 German bombers dropped 500 tons of explosives and nearly 900 incendiary bombs in ten hours of unrelenting bombardment on Coventry. The center of the city was destroyed as were more than 4,000 homes; three-quarters of the city's factories were damaged and more than 550 people were killed.

Many people were inadvertently injured by England's own self-defense efforts. Anti-aircraft missiles were the main source of shrapnel falling over London. In the early stages of the Blitz, it took an average of 30,000 shells to shoot down one Luftwaffe plane. Later, the defenders performed better, but the city was still bombarded by metal that was meant for the Germans.

More than 20,000 people were killed in the Blitz. The last night, May 10, 1941, was the worst; 3,000 Londoners were killed.

Though the bombing campaign caused great fear, damage, and death in England, it also weakened the Luftwaffe. When the raids on London began, the concentrations of German bombers became easier targets and the Luftwaffe spread its forces more thinly. By the end, it lost 650 aircraft and many irreplaceable pilots.